What I talk about in my teaching sessions

Month: December 2017

We recently suffered through an M&M meeting about a patient that presented with vertigo and hearing loss. While clinically a typical vestibular neuritis, the importance of sudden hearing loss was grossly understated, with arguments like “this is all the more a peripheral disease” and “belongs to EENT then, anyway”. I certainly grew up with a standard operating procedure that allowed to turf “vertigo + hearing loss” without further workup, unless there were signs or symptoms of CNS involvement.

In this blog entry, I try to work through the numbers, invoking some recent publications.

Unilateral sudden hearing loss (USHL)

(bilateral hearing loss is a different animal altogether)

more than 30 dB hearing reduction in < 3d (in at least three frequencies)

quite frequent ~ 27/100.000

usually middle aged

about a third have vertigo, depending on how strictly you define it

Causes

As in so many other cranial nerve dysfunctions we don’t really know the etiology of your average run-of-the-mill USHL. It usually seems to be benign, because otherwise people would be dying all over the place, so depending on your prejudices you can suspect anything from viral to vascular.

It is really quite surprising that these etiologically occult cases have been ascribed by some to vascular causes (without any proof except for risk factors) as if this were benign in any way, similar to cases of mononeuropathic cranial nerve dysfunctions such as trochlear, abducens or facial palsy where the “microvascular” theory is built on the epidemiologic association with risk factors such as hypertension and diabetes. If those entities were “microvascular”, we ought to treat them it with tPA, GP-IIb/IIIa inhibitors (analogously to microvascular stroke #lacune), or at least include them into a risk factor reduction program and ASS them.

The viral theory (which seems to be accepted for the case of bell’s palsy) is also difficult to establish – at least antivirals don’t seem to work.

There are plenty of cool differential diagnoses, such as Cogan’s or Syphilis (see this article for a table), but of course you cannot exclude all the zebras in the average case.

Differential diagnosis

So what is in the differential that is acutely endangering the patient and, in particular, what changes if vertigo is added to the symptoms?

Vertebrobasilar stroke – see below.

Acoustic neuroma: this needs to be recognized, but not acutely.

Migraine – not dangerous, but eminently treatable.

Blood problems – sickle cell, leukemia, … – it seems that an ESR and a CBC are enough.

Real infections: syphilis mainly, maybe HIV?

Then there are things that usually only EENT specialists care for, such as Meniere’s and perilymphatic fistulas, cholesteatomas and many more. All these seem to me to be not that urgent and therefore safe to send away, if symptoms have been covered.

The literature, being written by neurootologists (a quite intellectual bunch), stresses the differentiation between central and peripheral causes, with multiple sclerosis, migraine and stroke among the most frequent central causes. As an ED physician I would rather stress stroke as the main cause to be identified acutely, deferring the decision when to MRI vertigo patients to the clinic.

Acute vestibular syndrome plus hearing loss

About 3-15% of vertigo patients turn out to have a vascular problem, either a stroke or a TIA due to serious stenosis. Now in the past, neurologic myth had it that hearing symptoms (SHL or tinnitus) reduce this risk, so that it is safe to turf the patient to EENT. It turns out that the opposite is true – nearly double the amount: 5,5%1, at least in this recent population based survey, which should all but overestimate the risk.

I will try to give an explanation for this fact in a second.

First let us consider the practical implications. We have learned to filter acute vertigo patients (it is superbly unclear what acute means but for the sake of simplicity I assume this means < 3 weeks), using a good history and physical/neuro exam, including (but not limited to) the head thrust maneuver (aka head impulse test). Some would want to simplify this to HINTS or INFARCT, which amounts to reducing the rest of the neuro exam to nystagmus (direction changing?) and cover test (vertical disconjugation?), which in my humble opinion is too brief in the hands of a Neurologist. But even if you limit yourself to HINTS you miss at most 1 percent of strokes and thus improve on MRI (which misses up to 20-30% of strokes in the acute phase).

Why is that? The only way that a stroke mimics vestibular neuritis with a positive Halmagyi sign (Halmagyi-positive pseudoneuritis), is that it hits the nerve root entry zone around the fourth ventricle. And this region is highly collateralized as it can derive it’s blood supply from small perforators, AICA, PICA and even dural and petrosal arteries.

On the other hand, a true vestibular neuritis that causes permanent vertigo usually will cause the horizontal vestibuloocular reflex (hVOR) to suffer, except for the rare case of inferior vestibular neuritis (as opposed to your standard superior neuritis which affects nerve fibres to the horizontal canal) – this occurs in only 9 of 703 cases of vestibular neuritis overall according to this retrospective case series. So most of the patients should have impaired hVOR, yet not all of them are discovered during the clinical head impulse test, because covert saccades (fixation-correcting saccades during the thrust rather than afterwards) are impossible to see without videooculography and sometimes the hVOR impairment is not serious enough to cause correcting saccades at all. We don’t really know the percentage of covert saccades in real patients, but in dizziness clinics it can be up to 30%. Personally, I see way more covert correcting saccades with the slow motion app of my iphone, which has not been properly studied but definitely improves the clinical HIT as it makes it objective. One problem with all the investigations into sensitivities of neurootological testing vs. HIT is the lack of a gold standard – there is no other biomarker for vestibular neuritis than VOR (plus other sophisiticated vestibular lab tests) and this is defined by gain reduction (i.e. eye movement divided by ear movement) to 0,7 or less in the vestibular lab in order to preserve test quality indicators, so we might miss some cases with only slight VOR reduction.

Pseudolabyrinthitis: Acute vestibular syndrome with hearing loss due to ischemia

This corresponds to a stroke in the territory of the labyrinth artery, which usually (98%) derives from the AICA or the basilar artery (in the remaining cases it branches off the PICA, but this is exceedingly rare – see this 2015 case report) and does not have collaterals, so that it serves as a Letzte Wiese of the vertebrobasilar system. For instance, a high grade basilar artery stenosis (or equivalently a vertebral artery stenosis in the frequent case of hypoplastic contralateral supply) might cause temporary hearing loss and vertigo with nystagmus. Although the whole labyrinth is expected to suffer, the resulting nystagmus at least in part will be horizontal as in a status post labyrinthectomy.

Now we don’t know the percentage of AVS+HL patients that have a real vascular cause but the above mentioned case series suggests taking it even more seriously – this has lead to the so-called HINTS+ scheme, adding hearing loss to your AVS workup as harbinger for possible vascular (if not necessarily central) cause, without reducing specificity of your workup.

The odds

Between 5-25% of AVS pt. have a vascular cause

About 15-20% of vascular cause AVS are AICA in origin

68% of AICA strokes have auditory symptoms

50% of AICA strokes have a “falsely peripheral” HIT

Transient audiovestibular symptoms

What about the patients that had a serious vertigo spell but recover before you see them in the ER? Some have dubbed this entity ATVS – acute transient vestibular syndrome. It hasn’t been studied much yet, but from what has been said above we should conclude that it merits a proper TIA workup (even if vertigo itself does not count as a TIA symptom in most guidelines), including (at least clinical) vestibular testing – see below – and an MRI, possibly with MR-perfusion if you read this recent Stroke 2017 paper.

My vertigo workup

Do a proper history, asking explicitly about auditory symptoms and craniocervical pain. Take your time for that.